The uterus is a fibromuscular hollow organ situated between the bladder and the rectum. The uterus is divided into two portions: an upper muscular body, the corpus, and a lower fibrous cervix (Fig. 38-14). The transition between the corpus and the cervix is known as the uterine isthmus. This also marks the transition from endocervical canal to endometrial cavity. The portion of the corpus that extends above the entry level of the fallopian tubes into the endometrial cavity is known as the fundus.
Uterus, adnexa, and associated anatomy.
The shape, weight, and dimensions of the uterus vary according to parity and estrogen stimulation. Before menarche and after menopause, the corpus and cervix are approximately equal in size, but during the reproductive years, the uterine corpus is significantly larger than the cervix. In the adult, nonpregnant woman, the uterus measures approximately 7 cm in length and 5 cm in width at the fundus.
The uterus consists of an inner mucosal layer called the endometrium, which surrounds the endometrial cavity, and a thick muscular wall known as the myometrium. The endometrium consists of columnar epithelium and specialized stroma. The superficial portion of the endometrium undergoes cyclic changes with the menstrual cycle.
The spiral arterioles located in the endometrium undergo hormonally mediated constriction or spasm that promotes shedding of the superficial portion of the endometrium with each menstrual cycle. The deeper basalis layer of the endometrium is preserved after this shedding and is responsible for regeneration of a new superficial layer.
Peritoneal serosa overlies the uterus, except at two sites. First, the anterior portion of the cervix is covered by the bladder. Second, the lateral portions of the corpus and cervix attach to the broad and cardinal ligaments.
The uterine cervix begins caudal to the uterine isthmus and is approximately 3 cm in length. The wall of the cervix consists primarily of fibrous tissue and a smaller amount of smooth muscle. The smooth muscle is found on the cervical wall periphery and serves as the attachment point for the cardinal and uterosacral ligaments and for the fibromuscular walls of the vagina.
The attachments of the vaginal walls to the outer cervix divide it into a vaginal part known as the portio vaginalis and a supravaginal part known as the portio supravaginalis (see Fig. 38-14). The portio vaginalis is covered by nonkeratinizing squamous epithelium.
The endocervical canal is lined by columnar, mucus-secreting epithelium. The lower border of the canal, called the external cervical os, contains a transition from the squamous epithelium of the portio vaginalis to the columnar epithelium of the cervical canal. The exact location of this transition, termed the squamocolumnar junction, varies depending on hormonal status (Fig. 29-5). At the upper border of the endocervical canal is the internal cervical os, where the narrow cervical canal becomes continuous with the wider endometrial cavity.
The main support of the uterus and cervix is provided by the levator ani muscles and the connective tissue that attaches the outer cervix to the pelvic walls. The connective tissue that attaches lateral to the uterus and cervix on each side is called the parametrium and continues caudad along the vagina as the paracolpium. The parametrium consists of what is clinically known as the cardinal ligament and uterosacral ligament (Fig. 38-15).
Pelvic viscera and their connective tissue support. Relationship of the urethra, bladder trigone, and distal ureter to the anterior vaginal wall and to the uterine cervix.
The cardinal ligaments, also termed transverse cervical ligaments or Mackenrodt ligaments, consist primarily of perivascular connective tissue (Range, 1964). They attach to the posterolateral pelvic walls near the origin of the internal iliac artery and surround the vessels supplying the uterus and vagina.
The uterosacral ligaments insert broadly into the posterior pelvic walls and sacrum and form the lateral boundaries of the cul-de-sac of Douglas. These ligaments originate from the posterior inferior surface of the cervix, but may also originate, in part, from the proximal posterior vagina (Umek, 2004). They consist primarily of smooth muscle and contain some pelvic autonomic nerves (Campbell, 1950; Ripperda, 2015).
Clinically, during pelvic reconstructive surgeries that use the uterosacral ligaments as attachment sites for the vaginal apex, surrounding structures are especially vulnerable (Wieslander, 2007). Namely, the rectum lies medial to the uterosacral ligaments. The ureter, pelvic sidewall vessels, and sacral nerves run lateral to and close to these ligaments.
These ligaments are smooth muscle extensions of the uterine corpus and represent the homologue of the gubernaculum testis. The round ligaments arise from the lateral aspect of the corpus just below and anterior to the origin of the fallopian tubes. They extend laterally to the pelvic sidewall (see Fig. 38-14). They enter the retroperitoneal space and pass lateral to the inferior epigastric vessels before entering the inguinal canal through the internal inguinal ring. After coursing through the inguinal canal, the round ligaments exit through the external inguinal ring to terminate in the subcutaneous tissue of the labia majora (see Fig. 38-4). The round ligaments do not significantly contribute to uterine support. They receive their blood supply from a small branch of the uterine or ovarian artery known as Sampson artery.
Clinically, the location of the round ligament anterior to the fallopian tube can assist a surgeon during tubal sterilization through a minilaparotomy incision. This may be especially true if pelvic adhesions limit tubal mobility and thus hinder identification of fimbria prior to tubal ligation.
Division of the round ligament is typically an initial step in abdominal and laparoscopic hysterectomy. Its transection opens the broad ligament leaves and provides access to the pelvic sidewall retroperitoneum. This access allows direct visualization of the ureter and permits isolation of the uterine artery for safe ligation.
These ligaments are double layers of peritoneum that extend from the lateral walls of the uterus to the pelvic walls (see Fig. 38-14). Within the upper portion of these two layers, the fallopian tube, the ovarian ligament, and round ligament are found. Each of these has its separate mesentery, called the mesosalpinx, mesovarium, and mesoteres, respectively, which carry nerves and vessels to these structures. At the lateral border of the fallopian tube and the ovary, the broad ligament ends where the infundibulopelvic ligament, described later on this page, blends with the pelvic wall. The cardinal and distal uterosacral ligaments lie within the lower portion or “base” of the broad ligament.
The blood supply to the uterine corpus arises from the ascending branch of the uterine artery and from the medial or uterine branch of the ovarian artery (see Figs. 38-14 and 38-15). The uterine artery may originate directly from the internal iliac artery, or it may have a common origin with the internal pudendal or with the vaginal artery (see Fig. 38-12). The uterine artery approaches the uterus in the area of the uterine isthmus. Here, the uterine artery courses over the ureter and provides a small branch to it. Several uterine veins course along the side of the artery and are variably found over or under the ureter. The uterine artery then divides into a larger ascending and a smaller descending branch that course alongside the uterus and cervix, respectively. These vessels connect on the lateral border of the uterus but form an anastomotic arterial arcade that supplies the uterine walls (Fig. 8-3). The cervix is supplied by the descending or cervical branch of the uterine artery and by ascending branches of the vaginal artery.
Clinically, because the uterus receives dual blood supply from both ovarian and uterine vessels, some surgeons during myomectomy place tourniquets at both the infundibulopelvic ligament and uterine isthmus. This decreases blood flow from the ovarian and uterine arteries, respectively.
Uterine Lymphatic Drainage
Lymphatic drainage of the uterus is primarily to the obturator and internal and external iliac nodes (Fig. 38-16). However, some lymphatic channels from the uterine corpus may pass along the round ligaments to the superficial inguinal nodes, and others may extend along the uterosacral ligaments to the lateral sacral nodes.
Pelvic lymph nodes and the course of the ureter and ovarian vessels.
The uterus is innervated by fibers of the uterovaginal plexus, also known as Frankenhäuser ganglion. These fibers travel along the uterine arteries and are found in the connective tissue of the cardinal ligaments (see Fig. 38-13).
Ovaries and Fallopian Tubes
The ovaries and fallopian tubes constitute the uterine adnexa. The size and hormonal activity of the ovaries are dependent on age, stage of the menstrual cycle, and exogenous hormonal suppression. During reproductive years, the ovaries measure 2.5 to 5 cm in length, 1.5 to 3 cm in thickness, and 0.7 to 1.5 cm in width.
The ovaries consist of an outer cortex and an inner medulla. The ovarian cortex is made up of a specialized stroma punctuated with follicles, corpora lutea, and corpora albicantia. A single layer of mesothelial cells covers this cortex as a surface epithelium. The medullary portion of the ovary primarily consists of fibromuscular tissue and blood vessels. Vessels and nerves enter the medulla at the hilum, which is a depression along the mesenteric border of the ovary. The medial aspect of the ovary is connected to the uterus by the uteroovarian ligament (see Fig. 38-14). Laterally, each ovary is attached to the pelvic wall by an infundibulopelvic ligament, also termed suspensory ligament of the ovary, which contains the ovarian vessels and nerves.
The blood supply to the ovaries comes from the ovarian arteries, which arise from the anterior surface of the abdominal aorta just below the origin of the renal arteries and from the ovarian branches of the uterine arteries (see Fig. 38-16). The ovarian veins follow the same retroperitoneal course as the arteries. The right ovarian vein drains into the inferior vena cava, and the left ovarian vein drains into the left renal vein.
Lymphatic drainage of the ovaries follows the ovarian vessels to the lower abdominal aorta, where they drain into the paraaortic nodes. For their innervation, the ovaries are supplied by extensions of the renal plexus that course along the ovarian vessels in the infundibulopelvic ligament and variably by contributions of the inferior hypogastric plexus.
The fallopian tubes are tubular structures that measure 7 to 12 cm in length (see Fig. 38-14). Each tube has four identifiable portions. The interstitial portion passes through the body of the uterus at the region known as the cornua. The isthmic portion begins adjacent to the uterine corpus. It consists of a narrow lumen and a thick muscular wall. The ampullary portion is recognized as the lumen of the isthmic portion of the tube widens. In addition, this segment has a more convoluted mucosa. The fimbriated portion is the distal continuation of the ampullary segment. The fimbriated end has many frondlike projections that provide a wide surface area for ovum pickup. The fimbria ovarica is the extension that contacts the ovary.
The ovarian artery runs along the ovary’s hilum and sends several branches through the mesosalpinx to supply the fallopian tubes (see Fig. 38-14). The venous plexus, lymphatic drainage, and nerve supply of the fallopian tubes follow a similar course to that of the ovaries.
The vagina is a hollow viscus whose shape is determined by the structures that surround it and by the attachments of its lateral walls to the pelvic walls. The distal portion of the vagina is constricted by the action of the levator ani muscles (see Fig. 38-10). Above the pelvic floor, the vaginal lumen is more capacious and distensible. In the standing or anatomic position, the apex of the vagina is directed posteriorly toward the ischial spines, and the upper two thirds of the vaginal tube lie almost parallel to the plane of the levator plate. Although variable, the average length of the anterior vaginal wall is 7 cm and that of the posterior wall is 9 cm. The recesses within the vaginal lumen in front of and behind the cervix are known as the anterior fornix and posterior fornix, respectively (Fig. 38-17). The vaginal walls consist of three layers: (1) adjacent to the lumen, a layer of nonkeratinized squamous epithelium with an outer lamina propria; (2) a muscular layer of smooth muscle, collagen, and elastin; and (3) an outer adventitial layer of collagen and elastin (Weber, 1995, 1997). These latter two form the fibromuscular component of the vagina.
Surgical cleavage planes and vaginal wall layers.
The vagina lies between the bladder and rectum and, along with its connections to the pelvic walls, provides support to these structures (see Figs. 38-15 and 38-17). The vagina is separated from the bladder anteriorly and the rectum posteriorly by the vaginal adventitia. The lateral continuation of this adventitial layer contributes the paravaginal tissue that attaches the walls of the vagina to the pelvic walls. This paravaginal tissue constitutes the paracolpium. This tissue consists of loose areolar and fatty tissue containing blood vessels, lymphatics, and nerves. The anterior fibromuscular vaginal wall and its paravaginal attachments to the arcus tendineus fascia pelvis represent the layer that supports the bladder and urethra and is clinically referred to as pubovesicocervical fascia (see Fig. 38-15).
The lateral attachments of the posterior vaginal walls are to the fascia covering the upper surface of the levator ani muscles. The posterior vaginal wall and its connective tissue attachments to the sidewall support the rectum. This layer is clinically known as the rectovaginal fascia or fascia of Denonvilliers. However, similar to microscopic findings of the anterior vaginal wall, histologic studies have failed to show a separate layer between the posterior wall of the vagina and the rectum except in the distal 3 to 4 cm. Here, the dense fibromuscular tissue of the perineal body separates these structures (DeLancey, 1999).
Surgically, dissections in the anterior vaginal wall or in the posterior vaginal wall separate portions of the vaginal muscularis from the epithelium for surgeries such as anterior and posterior colporrhaphy. In contrast, posterior or anterior access to the coccygeus-sacrospinous ligament complex is accomplished by incising the full thickness of the anterior or posterior fibromuscular wall of the vagina, respectively. This deeper dissection allows access to the vesicovaginal or rectovaginal space and lateral dissection from these spaces allows access to the pararectal space. Because there is no true histologic “fascial” layer between the vagina and the bladder and between the vagina and the rectum, some recommend that terms such as “pubocervical/pubovesical fascia” or “rectovaginal fascia” be abandoned. They propose that these be replaced by more accurate descriptive terms such as vaginal muscularis or fibromuscular layer of the anterior and posterior vaginal walls.
Vesicocervical and Vesicovaginal “Potential” Spaces
The vesicocervical space begins below the vesicouterine peritoneal fold or reflection, which represents the loose attachments of the peritoneum in the anterior cul-de-sac (see Figs. 38-17 and 38-18). The vesicocervical space continues down as the vesicovaginal space, which extends to the junction of the proximal and middle thirds of the urethra. Below this point, the urethra and vagina fuse.
Connective tissue and surgical spaces of the pelvis.
Clinically, during an abdominal hysterectomy or cesarean delivery, surgeons easily lift and incise the vesicouterine peritoneal fold to create a bladder flap and then open the vesicocervical space. For vaginal hysterectomy, the distance between the anterior vaginal fornix and the anterior cul-de-sac peritoneum spans several centimeters. Thus, to successfully enter the peritoneal cavity anteriorly, proper identification and sharp dissection of the loose connective tissue that lies within the vesicovaginal and then vesicocervical spaces is necessary (see Fig. 38-17) (Balgobin, 2011).
This is adjacent to the posterior surface of the vagina. It extends from the cul-de-sac of Douglas down to the superior border of the perineal body, which extends 2 to 3 cm cephalad to the hymeneal ring (see Figs. 38-17 and 38-18). Rectal pillars, also known as the deep uterosacral or rectouterine ligaments, are fibers of the cardinal-uterosacral ligament complex that extend down from the cervix and attach to the upper portion of the posterior vaginal wall. These fibers connect the vagina to the lateral walls of the rectum and to the sacrum. These pillars also separate the midline rectovaginal space from the more lateral pararectal spaces.
Clinically, the rectovaginal space contains loose areolar tissue and is easily opened with finger dissection during abdominal surgery (see Fig. 38-18). Perforation of the rectal pillar fibers allows access to the sacrospinous ligaments used in vaginal suspension procedures.
The posterior cul-de-sac peritoneum extends down the posterior vaginal wall 2 to 3 cm inferior to the posterior vaginal fornix (Kuhn, 1982). Thus, during vaginal hysterectomy, in contrast to anterior peritoneal cavity entry, entering the peritoneal cavity posteriorly is readily done by incising the vaginal wall in the area of the posterior fornix (see Fig. 38-17).
The main support of the vagina is provided by the levator ani muscles and the connective tissue that attaches the lateral walls of the vagina to the pelvic walls. These attachments are the cardinal and uterosacral ligaments. Although the visceral connective tissue in the pelvis is continuous and interdependent, DeLancey (1992) has described three levels of vaginal connective tissue support that help explain pelvic support dysfunction.
For upper vaginal support, the parametrium continues caudally down the vagina as the paracolpium (see Fig. 38-15). This tissue attaches the upper vagina to the pelvic wall, suspending it over the pelvic floor. These attachments are known as level I support or suspensory axis and provide connective tissue support to the vaginal apex after hysterectomy. In the standing position, level I support fibers are vertically oriented. Clinical manifestations of level I support defects include uterine prolapse or posthysterectomy vaginal vault prolapse.
For midvaginal support, the lateral walls of the vagina’s midportion are attached to the pelvic walls on each side by visceral connective tissue known as endopelvic fascia. These lateral attachments of the vaginal walls blend into the arcus tendineus fascia pelvis and to the medial aspect of the levator ani muscles, and in doing so create the anterior and posterior lateral vaginal sulci (see Fig. 38-15). These grooves run along the vaginal sidewalls and give the vagina an “H” shape when viewed in cross section. As noted earlier, the arcus tendineus fascia pelvis covers the medial aspect of the obturator internus and levator ani muscles. It spans from the inner and lower surface of the pubic bones to the ischial spines (see Figs. 38-7 and 38-15).
Attachment of the anterior vaginal wall to the levator ani muscles is responsible for the bladder neck elevation noted with cough or Valsalva maneuver (see Fig. 38-10). Thus, these midvaginal attachments may have significance for stress urinary continence and are referred to as level II support or the attachment axis. Clinical manifestations of level II support defects include anterior and posterior vaginal wall prolapse and stress urinary incontinence.
For distal vaginal support, the distal third of the vagina is directly attached to its surrounding structures (see Fig. 38-9). Anteriorly, the vagina is fused with the urethra. Laterally it attaches to the pubovaginalis muscle and perineal membrane, and posteriorly to the perineal body. These vaginal attachments are referred to as level III support or the fusion axis and are considered the strongest of the vaginal support components. Clinically, failure of this level of support can result in distal rectoceles or perineal descent. Anal incontinence may also result if the perineal body is absent, as may follow obstetric trauma.
Vaginal Blood Supply, Lymphatics, and Innervation
The main blood supply to the vagina arises from the descending or cervical branch of the uterine artery and from the vaginal artery, a branch of the internal iliac artery (see Fig. 38-12). These vessels form an anastomotic arcade along the lateral sides of the vagina at the level of the vaginal sulci. They also anastomose with the contralateral vessels at points on the anterior and posterior walls of the vagina. Additionally, the middle rectal artery from the internal iliac artery contributes to the posterior vaginal wall supply. The distal walls of the vagina also receive contributions from the internal pudendal artery. Lymphatic drainage of the upper two thirds of the vagina is similar to that of the uterus as described on page 809. The distal part of the vagina drains with the vulvar lymphatics to the inguinal nodes. A more detailed description of the vulvar lymphatics is presented on page 822. Last, vaginal innervation comes from inferior extensions of the uterovaginal plexus, a component of the inferior hypogastric plexus (see Fig. 38-13).
Lower Urinary Tract Structures
The bladder is a hollow organ that stores and evacuates urine (Fig. 38-19). Anteriorly, the bladder rests against the inner surface of the pubic bones and then, as it fills, also against the anterior abdominal wall. Posteriorly, it rests against the vagina and cervix. Anteroinferiorly and laterally, the bladder contacts the loose connective and fatty tissue that fills the retropubic space, and here, the bladder lacks a peritoneal covering. The reflection of the bladder onto the abdominal wall is triangular, and the triangle apex is continuous with the median umbilical ligament.
Midsagittal view of pelvic structures and associated anatomy. L4 = fourth lumbar vertebra; PS = pubic symphysis; S1, S3 = first and third sacral vertebrae.
Clinically, an intentional cystotomy can be made to confirm patency of the ureteral orifices, to assist with surgical dissection, or to place ureteral stents. The incision is ideally placed in the retropubic extraperitoneal portion of the bladder close to the apex. This avoids direct contact between the abdominopelvic viscera and the cystotomy site and minimizes the risk of fistula formation.
The bladder wall consists of coarse bundles of smooth muscle known as the detrusor muscle, which extends into the upper part of the urethra. Although separate layers of the detrusor are described, they are not as well defined as the layers of other viscous structures (Fig. 23-1). The innermost layer of the bladder wall is plexiform, which can be seen from the pattern of trabeculations noted during cystoscopy. The mucosa of the bladder consists of transitional epithelium and underlying lamina propria. A submucosal layer intervenes between this mucosa and the detrusor muscle.
The bladder is divided into a dome and a base approximately at the level of the ureteral orifices. The dome is thin walled and distensible, whereas the base is thicker and undergoes less distention during filling (see Fig. 38-15). The bladder base consists of the vesical trigone and the detrusor loops. These loops are two U-shaped bands of fibers found at the vesical neck, where the urethra enters the bladder wall. Ureteral orifices lie within the trigone and empty here into the bladder. The pelvic ureter courses in the pelvic sidewall retroperitoneum and is discussed on page 816.
The blood supply to the bladder arises from the superior vesical arteries, which are branches of the patent portion of the umbilical artery. Other contributors are the middle and inferior vesical arteries, which, when present, often arise from either the internal pudendal or the vaginal arteries (see Fig. 38-12). The nerve supply to the bladder arises from the vesical plexus, a component of the inferior hypogastric plexus (see Fig. 38-13).
The female urethra measures 3 to 4 cm in length. The urethral lumen begins at the internal urinary meatus within the bladder, and then courses through the bladder base for less than a centimeter. This region where the urethral lumen traverses the bladder base is called the bladder neck. The distal two thirds of the urethra are fused with the anterior vaginal wall.
The walls of the urethra begin outside the bladder wall. They consist of two layers of smooth muscle, an inner longitudinal and an outer circular, which are in turn surrounded by a circular layer of skeletal muscle referred to as the sphincter urethrae or rhabdosphincter (Fig. 38-20). Approximately at the junction of the middle and lower third of the urethra, and just above or deep to the perineal membrane, two strap skeletal muscles called the urethrovaginal sphincter and compressor urethrae are found. These muscles were previously known as the deep transverse perineal muscles in females. Together with the sphincter urethrae, they constitute the striated urogenital sphincter complex. Together, these three muscles function as a unit and have a complex and controversial innervation. Their fibers act cumulatively to supply constant tonus and to provide emergency reflex activity mainly in the distal half of the urethra to sustain continence.
Urethra and associated muscles.
Distal to the depth of the perineal membrane, the walls of the urethra consist of fibrous tissue, serving as the nozzle that directs the urine stream. The urethra has a prominent submucosal layer that is lined by hormonally sensitive stratified squamous epithelium (Fig. 23-8). Within the submucosal layer on the dorsal (vaginal) surface of the urethra is a group of glands known as the paraurethral glands, which open into the urethral lumen (Fig. 26-3). Duct openings of the two most prominent glands, termed Skene glands, are seen on the inner surface of the external urethral orifice.
The urethra receives its blood supply from branches of the inferior vesical/vaginal and internal pudendal arteries. Although still controversial, the pudendal nerve is believed to innervate the most distal part of the striated urogenital sphincter complex. Somatic efferent branches from S2–S4 that course along the inferior hypogastric plexus variably innervate the sphincter urethrae. An additional discussion of lower urinary tract innervation is found in Chapter 23.
Clinically, chronic infection of the paraurethral glands can lead to urethral diverticula. Due to the multiple openings of these glands along the length of the urethra, diverticula may develop at various sites along the urethra.
The rectum is continuous with the sigmoid colon approximately at the level of the third sacral vertebra (see Fig. 38-19). It descends on the anterior surface of the sacrum for approximately 12 cm and ends in the anal canal after passing through the levator hiatus. The anterior and lateral portions of the proximal two thirds of the rectum are covered by peritoneum. The peritoneum is then reflected onto the posterior vaginal wall to form the posterior cul-de-sac of Douglas, also termed rectouterine pouch. In women, the cul-de-sac is located approximately 5 to 6 cm from the anal orifice and can be palpated manually during rectal or vaginal examination. At its commencement, the rectal wall is similar to that of the sigmoid, but near its termination it becomes dilated to form the rectal ampulla, which begins below the posterior cul-de-sac peritoneum.
The rectum contains several, usually three, transverse folds called the plicae transversales recti, also termed valves of Houston (Fig. 38-21). The largest and most constant of these folds is located anteriorly and to the right, approximately 8 cm from the anal orifice. These folds may contribute to fecal continence by supporting fecal matter above the anal canal. Clinically, in the empty state, the transverse rectal folds overlap each other, making it difficult at times to manipulate an examining finger or endoscopy tube past this level.
Ischioanal fossa and anal sphincter complex.